Having recently run the Thanet Quicksand I think it deserves a mention. This is a fifteen mile race run at low tide in late summer - early autumn. Generally a beach race with some clifftop running, the race involves running across sand (predictably) both hard & soft, rocks, shingle, seaweed, rocks covered in seaweed plus a couple of scrambles up the cliffs. In short the beach sections are either physically draining or quite tricky underfoot but nonetheless, enjoyable!
